The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
High power uninterruptible power supplies are used in supplying power to a facility, or areas of a facility. A high power uninterruptible power supply (“UPS”) may have a one mega-volt-amp (MVA) capacity or above. In a facility, an electric utility substation down converts utility power to generate substation power that is supplied to the UPS, which conditions the substation power. The UPS has a source of back-up power that provides power in the event of an interruption in the utility power.
Referring now to FIG. 1, a power distribution system 10 that includes a high power UPS 12 is shown. The power distribution system 10 includes a utility substation 14 that includes a utility transformer that down converts (steps down) a utility voltage (e.g. 12 kilovolts alternating current (KVAC) to 34.5 KVAC) to a substation voltage (e.g. 480 VAC). The UPS 12 provides uninterruptible power with a load voltage (e.g. 480 VAC) to a load 15.
The UPS 12 includes an input transformer 16, a rectifier 18, an inverter 20 and an output transformer 22. The input transformer 16 may include a primary winding and a secondary winding. The primary winding receives the substation voltage. It should be understood that the primary winding and the secondary winding may include a plurality of individual windings. For example, in a three-phase system, the primary winding may illustratively be “wye” configured winding” having a winding for each phase and the secondary winding may also be a “wye” configured winding having a winding for each phase. The secondary winding is connected to the rectifier 18 that converts the substation voltage to a first direct current (DC) voltage (e.g. 540 VDC). The inverter 20 receives the first DC voltage and/or a second DC voltage from a DC back-up power source 24.
The inverter 20 converts a DC voltage received from the rectifier 18 or from the DC back-up power source 24 to an AC voltage (e.g. 250V AC) that is supplied to the output transformer 22. The output transformer 22 includes primary and secondary windings, which up convert (boost) the AC voltage to an output voltage (e.g. 480 VAC) that is provided to the load 15. The output transformer 22 is fully rated, as approximately 100% of the current that is provided from the inverter 20 passes through windings of the output transformers 22.
The UPS 12 may include a bypass switch 25, which may be used to bypass the input transformer 16, the rectifier 18, the inverter 20, and the output transformer 22 and provide bypass power to the load 15. The bypass power may be provided through the bypass switch 25 and may be the power from the utility substation 14.